Conventional earth current leakage circuit breakers and over-current fuses are commonly deployed to prevent injuries to people and property from dangerous conditions resulting from, for example, current leakages or severe current arcs. Although such devices detect the occurrence of some electrical faults to prevent harm to persons and property, even when such conventional devices are employed, certain electrical faults are not detected. For example, as conventional devices lack intelligent characteristic and physical fault signature identification, certain current arc occurrences might not be detected: This presents potential fire hazards.
A current arc is typically caused by a current surging over separated or poorly contacting electrical surfaces within electrical equipment, for example, in its power cord or in an electrical device itself; or within damaged electrical wiring, such as, within the walls of a building. Current arc electrical faults may be defined as current through ionized gas between the two (e.g., supply-side and load-side) separated or poorly contacting electrical surfaces. Such current arcs are often characterized by sparking and extremely high heat, and as a result can cause electrical fires. For example, electrical fires may start when the heat and/or sparking of a current arc causes insulating material or construction material in the vicinity of the electrical fault to combust. Current arc-caused electrical fires may damage property or even endanger human life.
Unfortunately, conventional circuit breakers, fuses, or Ground Fault Circuit Interrupter (GFCI) protection devices typically cannot detect—and consequently halt—current arc electrical faults, unless a current arc produces sufficient current leakage to the electrical ground to be detected by a GFCI and/or results in a sufficient current imbalance to be detected by leakage current coil circuit. Typically, an arc fault does not involve current leaking to a ground conductor or any conducting devices to the ground; it is therefore unlikely to result in a substantial current imbalance between the supply and the load.
Underwriters Laboratories (UL), an American Worldwide Safety Consulting and Certification Organization, characterizes arc faults into two fundamental types, series arc faults and parallel arc faults. Parallel arcing typically refers to arcing that occurs between two conducting wires, or between a conductor and the ground. That is, the electrical fault may be in parallel with the electrical load. The instantaneous current of a parallel arc may be limited by, for example, the impedance of the voltage source, the properties of the wiring, and the nature of surfaces where the arc occurs. When such a parallel arc occurs, a conventional circuit breaker may trip very quickly, reducing the likely of damage caused by heating of the conducting wire or fire damage at the arc occurrence point. However, there are instances where a parallel arc may destroy faulted components and thereby create a large parallel arc voltage. Under such circumstances, the arc fault current may be below the tripping point of conventional current protection devices. Thus, such a dangerous parallel arc may avoid detection, and ultimately cause an electrical fire or other dangerous situation.
Series arcing typically refers to arcing that occurs between an electrical supply and an electrical load. That is, the electrical fault may be in series with the electrical load. This may be caused by, for example, corrosion in a pin-socket or a loose connection in contacting surfaces. For example, a series arc may be initially characterized by a voltage drop of, for example, a magnitude of several hundred mV across a poorly contacting connection, which may gradually heat up, oxidize, and/or pyrolize the materials or structure surrounding the electrical fault. If the series arc fault is permitted to persist, its voltage drop may increase to a magnitude of a few volts, consequently resulting a more dramatic increase in temperature, which may cause a release of smoke from surrounding polymer insulation and/or a fire. Generally, the current of a series arc is typically limited to a moderate value by the impedance of the electrical load of the circuit. As such, the peak current of a series arc might typically never exceed the design load current of an appliance providing an electric load, making the detection of a series arc fault particularly difficult. Thus, while the amount of power generated by series arc fault is typically less than that of a parallel arc fault, the detection of series arc faults poses additional challenges.
Therefore, there is a need to be able to identify and detect potential current arc electrical faults, and subsequently interrupt the connecting circuit to prevent potential current arc fire hazards. An apparatus that addresses arc faults may be referred to as an Arc Fault Circuit Interrupter (AFCI). Despite the existence of conventional AFCIs, there remains room for improvement in the technology. In order to accurately identify, detect, and halt dangerous arc faults, there remains a need to automatically classify potential arc current patterns and cause a circuit tripping mechanism to terminate the supply of electrical current when appropriate. Additionally, there remains a need for a tripping mechanism to support ensure a proper, flexible trip operation in time desired. There further remains a need for such a tripping mechanism to provide automatic and/or manual testing functionality to ensure that the AFCI and/or other electrical protection devices work properly.
It may be desirable that a successful detection of an arc fault conduction activates a tripping mechanism to enable a tripped state, wherein an AFCI apparatus is placed in an off or non-conductive state. It may also be desirable that an AFCI apparatus may detect an end-of-life (EOL) condition and consequently engage a permanent EOL state, where an AFCI is tripped and no further reset operation is possible.